The target_blaster entity is simply blaster fire that can be triggered. What I mean by blaster fire is like when you shoot the your blaster(1st weapon) or your hyperblaster. I didn't really notice many times in the id levels where these were used. The only level I remember seeing this entity is the first secret level. Anyhow, it's very simple and there are numerous uses for it.

The first thing you need to do is create the gun or whatever that is going to shoot the blaster fire. You don't really need to make it if you don't want to if though.

Next thing you do is place the target_blaster entity where you want the blaster fire to originate from.

There are a few key value pairs and spawnflags that you can set to make the target_blaster act in different ways. The key value pairs are angle, damage, and speed. angle determines the direction the target_blaster will fire. damage is of course the amount of damage the blast will take off when it hits another entity. speed is how fast the blaster fire will travel.

The different spawnflags for the target_blaster are notrail
and noeffects. I tried both
of these and did'nt really notice a difference between them
but I'm sure that there is a minor visual difference when one
or both of these spawnflags are turned on. I take it the notrail
makes the blaster fire not have a trail and noeffects
gets rid of the sparks. I'm not sure though. As I said, I didn't
really see a difference.

There is one more trick to getting your target_blaster into
working order. You must have some sort
of entity that will trigger the target_blaster to work.
This can be a multiple of entities. It all depends on how you
want to use the target_blaster. If you want it to shoot when
someone walks in front of it then you will need to use a trigger_multiple.
If you want it to shoot and wait 2 seconds, shoot and wait 2
seconds, etc, etc, then you will want to you a func_timer.
If you want it to start on and just keep on shooting forever
then use a trigger_always.
I could name a bunch more but I think you get the idea. As always
if you have any other questions please post them in the discussion
board.